It is known that cyclones are employed at the end of pneumatic conveyor plants for the separation of the air from the conveyed material. The separation may be more or less perfect as a function of the transported material and, anyway, normally the separated air drags with itself small portions of the material itself, without causing particular problems since that air can be safely filtered after its exit from the cyclone.
When materials are pneumatically transported which are light and have a relatively large size, such as plastic in film, it may happen, however, that because of air vortices or other, some sheets, even having a relatively large size, will exit from the cyclone together with the air, and such an occurrence will create extremely serious problems, both if this material will reach the electric exhaust fan and if it will reach the filter. It is obvious, indeed, that the material reaching into the electric exhaust fan will cause damages to the electric exhaust fan itself and, if it will reach the filter, the material could arrange itself in such a way to obstruct completely the filter, so stopping the passage of the air.
These drawbacks cause the shutdown of the plant and the corresponding prolongation of the working schedule, with consequences which are, also from this standpoint, economically heavy.